The present invention relates to inflatable medical devices. More specifically, the present invention relates to protecting medical devices during sterilization by providing automatic venting at high temperatures.
The laryngeal mask airway device is a well known device that is useful for establishing airways in unconscious patients. FIG. 1 shows a perspective view of a prior art laryngeal mask airway device 100. Laryngeal mask airway devices such as device 100 are described for example in U.S. Pat. No. 4,509,514. Device 100 includes a hollow airway tube 110 and an inflatable mask portion 130. Tube 110 extends from a proximate end 112 to a distal end 114 and defines an interior airway lumen that extends through the tube from the proximate end 112 to the distal end 114. Mask portion 130 defines, at least when inflated, a central opening 136. Mask portion 130 is coupled to the airway tube such that the lumen of the airway tube communicates with the mask portion""s central opening and such that the device 100 provides a sealed internal passage that extends from the proximate end 112 to opening 136.
In operation, the mask portion 130 is deflated, and then the mask portion is inserted through a patient""s mouth into the patient""s pharynx. The mask portion is preferably positioned so that a distal end 140 of mask portion 130 rests against the patient""s normally closed esophagus and so that the opening 136 of the mask portion 130 is aligned with the entryway of the patient""s trachea (i.e., the patient""s glottic opening). After the mask portion is so positioned, the mask portion is inflated thereby forming a seal around the patient""s glottic opening and this establishes a sealed airway extending from the proximate end 112 of the tube 110 to the patient""s trachea. The proximate end 112, which remains outside the patient, may be coupled to a ventilator for providing ventilation to the patient""s lungs.
Referring again to FIG. 1, laryngeal mask airway device 100 also includes an inflation tube 138 for permitting selective inflation or deflation of mask portion 130. An inflation valve 150 is connected to the proximate end of the inflation tube 138 and the distal end of inflation tube 138 is connected to the mask portion. The inflation valve 150 is normally closed so as to maintain the current pressure in mask portion 130. However, valve 150 may be opened to permit inflation or deflation mask portion 130.
FIG. 2A shows a sectional view of inflation valve 150, when the valve is closed (or when fluid may not freely flow between a first end 152 of the valve and a second end 154 of the valve). FIG. 2B shows a sectional view of inflation valve 150, when the valve is open (or when fluid may freely flow between first and second ends 152, 154). FIG. 2C shows a view of the first end 152 of valve 150 taken in the direction of arrow 2Cxe2x80x942C as shown in FIG. 2A. FIG. 2D shows an exploded sectional view of inflation valve 150, in which, for convenience of illustration, the space between opposite sectional views of body 160 has been artificially enlarged. FIG. 2E shows a more detailed sectional view of a typical prior art inflation valve 150, when the valve is closed.
As shown, inflation valve 150 includes a hollow body 160, which defines a central channel 169 that extends entirely through the body from end 152 to end 154. Valve 150 also includes a movable member, or pin, 170, and a spring 180, both of which are disposed within the central channel 169 of hollow body 160. One end 182 of spring 180 contacts a shoulder 162 of body 160. The other end 184 of spring 180 contacts a shoulder 172 of pin 170. The spring biases pin 170 away from shoulder 162 (or upwards as shown in FIGS. 2A, 2B, and 2D) such that a shoulder 174 of pin 170 normally contacts a shoulder 164 of body 160.
In the normal resting position of valve 150 (shown in FIG. 2A), contact between shoulder 174 (of pin 170) and shoulder 164 (of body 160) forms a seal and effectively prevents fluid from passing through channel 169 between the first end 152 and the second end 154 of valve 150 thereby closing the valve. The position of pin 170 shown in FIG. 2A may be regarded as a xe2x80x9cclosed positionxe2x80x9d. As shown in FIG. 2B, valve 150 may be opened by biasing pin 170 such that shoulder 174 (of pin 170) is separated from shoulder 164 (of body 160). Valve 150 is xe2x80x9copenxe2x80x9d as soon as shoulders 174 and 164 separate from one another. Once valve 150 is open, fluid may pass through channel 169 between the first end 152 and the second end 154 of valve 150 (i.e., fluid may pass from the first end to the second end or from the second end to the first end depending upon relative pressures at the valve ends). Any position of pin 170 in which shoulder 174 (of pin 170) is separated from shoulder 164 (of body 160) may be regarded as an xe2x80x9copen positionxe2x80x9d. If biasing of pin 170 continues, a shoulder 176 (of pin 170) eventually contacts a shoulder 166 (of body 160). Shoulder 166 serves to limit the motion of pin 170 such that once shoulders 176 and 166 contact one another, further movement of pin 170 (in a direction that continues to separate shoulders 174 and 164 from one another) is prevented. Unlike shoulders 174 and 164, the shoulders 176 and 166 do not form sealing surfaces, such that valve 150 is open even when shoulders 176 and 166 are in contact.
In laryngeal mask airway devices, the second end 154 of valve 150 is normally connected to the inflation line 138 (shown in FIG. 1). The valve 150 is normally closed so that if the mask portion 130 is inflated or pressurized, valve 150 maintains the pressure in the mask portion, or prevents gas in mask portion 130 from passing through valve 150 and escaping to the atmosphere external to the device. In its normally closed position, valve 150 also prevents mask portion 130 from spontaneously inflating after mask portion 130 has been intentionally deflated. Although it is normally closed, valve 150 may be temporarily opened to permit selective inflation and deflation of mask portion 130. Normally, an air syringe, or other air supply device (not shown), is coupled to end 152 of valve 150, and in the act of coupling, the air supply device biases the pin 170 so as to separate shoulders 174 (of pin 170) and 164 (of body 160) and thereby open the valve. The air supply device may then inflate or deflate mask portion 130. Once the air supply device is decoupled from valve 150, the biasing force provided by spring 180 automatically closes valve 150 and thereby maintains the current pressure inside of mask portion 130. End 152 of valve 150 is normally designed to comply with International Standard ISO 594-1 so that it may readily be coupled to standard air supply devices.
Although valves such as valve 150 have been in use for many years and have functioned well, there remains a need for providing improved control over the pressure in the inflatable portions of laryngeal mask airway devices as well as in other inflatable devicies.
These and other objects are provided by improved inflation valves and by inflatable devices constructed using those valves.
Several varieties of laryngeal mask airway devices are durable enough to permit them to be sterilized in an autoclave and reused. For example, the xe2x80x9cClassicxe2x80x9d laryngeal mask airway device sold by the Laryngeal Mask Company of Cyprus, is guaranteed to survive forty sterilizations, and in practice these devices may generally be sterilized (and reused) more than forty times before becoming too worn for reuse. The xe2x80x9cProsealxe2x80x9d, also sold by the Laryngeal Mask Company of Cyprus, may also be sterilized and reused.
The sterilization process normally involves exposing the laryngeal mask airway device to a high temperature environment inside an autoclave. The pressure of the environment inside an autoclave typically varies during the sterilization process such that at times the pressure is relatively high and at other times the pressure is relatively low. Laryngeal mask airway devices are normally fully deflated before being placed inside an autoclave for sterilization. If the devices are not fully deflated prior to sterilization, air trapped inside the mask portion can cause the mask portion to expand when the environment inside the autoclave is at a low pressure. Such expansion can sometimes cause the mask portion to burst thereby rendering the laryngeal mask airway device useless. Also, even if the mask portion doesn""t burst, excessive expansion of the mask portion within an autoclave may weaken or permanently deform the mask portion thereby decreasing the device""s useful life or potentially reducing the device""s usefulness.
One problem with prior art laryngeal mask airway devices is that practitioners cannot be relied upon to deflate them sufficiently to prevent potentially damaging expansion of the mask portion during sterilization in an autoclave. Also, if a laryngeal mask airway device is exposed to normal atmospheric pressure for several hours after a full deflation, the semi-permeable nature of most mask portions allow them to partially inflate. Such partial inflation can also result in potentially damaging expansion of the mask portion during subsequent sterilization. These problems are most serious for laryngeal mask airway devices that use a relatively soft material for the mask portion (e.g., such as the Proseal). However, the problem potentially affects any reusable (i.e., sterilizable) inflatable device.
The invention provides improved inflation valves and inflatable devices constructed with such valves. Valves constructed according to the invention automatically open when exposed to high temperatures. Accordingly, when a laryngeal mask airway device, or other inflatable device (such as an endotracheal tube, a tracheostomy tube, or a balloon catheter), equipped with a valve constructed according to the invention is sterilized, the valve will advantageously automatically open when exposed to the high temperature environment of the autoclave. This allows any gas that may have been previously trapped in the inflated portion of the device to escape through the valve into the autoclave chamber during low pressure portions of the sterilization process. Valves constructed according to the invention thereby automatically protect the inflatable portion of medical devices from undue expansion and wear.
In one aspect, the invention provides a laryngeal mask airway device comprising an airway tube, an inflatable mask portion, and a valve. The airway tube can extend from a proximate end,to a distal end. The inflatable mask portion can be fixed to the airway tube. The mask portion can be insertable through the mouth of a patient to an inserted location within the patient. The mask portion can form a seal around the patient""s glottic opening when the mask portion is in the inserted location and inflated. The proximate end of the airway tube can be disposed outside the patient when the mask portion is in the inserted location. The valve can be in fluid communication with the inflatable mask portion. The valve can include a member that is movable between an open position and a closed position. The valve can prevent fluid from escaping the mask portion when the member is in the closed position. The valve can permit fluid to escape the mask portion when the member is in the open position. The valve can include a resilient element. The resilient element can provide a first force that biases the member towards the closed position. The valve can include a temperature sensitive element. The temperature sensitive element can generate a second force that biases the member towards the open position. The first force can be greater than the second force when the ambient temperature is below a first value. The first force can be smaller than the second force when the ambient temperature is above a second value. An end portion of the member can be accessible to an environment external to the valve. The member can be movable to the open position by applying pressure to the end portion of the member.
In this aspect, the second force can be substantially equal to zero when the ambient temperature is below the first value.
Also in this aspect, the temperature sensitive element can comprise a nickel titanium alloy.
Also in this aspect, the temperature sensitive element can be characterized by a first length when the ambient temperature is below the first value, and the temperature sensitive element can be characterized by a second length when the ambient temperature is above the second value, the first length being longer than the second length.
Also in this aspect, the valve can include a body, the body defining an internal passage that extends through the body. Also, the body can further define a first shoulder. Also, the member can define a second shoulder, the first and second shoulders being in contact when the member is in the closed position, the first and second shoulders being spaced apart when the member is in the open position. Also, the device can include a cap fixed to one end of the body. Also, the device can include a post fixed to one end of the member. Also, the temperature sensitive element can have a first end, a second end, and a central portion, the first and second ends of the temperature sensitive element being fixed to the cap, the central portion of the temperature sensitive element contacting the post. Also, the post can define a slot, the central portion of the temperature sensitive element extending through the slot. Also, the cap can include a base, a body, and at least one clamp. Also, the clamp can be disposed between a portion of the base and a portion of the body. Also, an end of the temperature sensitive element can be fixed to the clamp. Also, the member can be disposed in the internal passage. Also, an end of the member can be proximate to an open end of the valve. Also, the second value can be greater than or equal to seventy degrees Celsius.
In another aspect, the invention provides a medical device comprising a tube, an inflatable structure, an inflation lumen, and a valve. The tube can define an interior passage. The inflatable structure can be fixed to the tube. The inflatable structure can be insertable into an airway of a human patient. The inflatable structure can form a seal with a portion of the airway when inserted into the patient and inflated. The inflation lumen can have a first end and a second end. The first end of the inflation lumen can be coupled to the inflatable structure. The valve can be coupled to the second end of the inflation lumen. The valve can define a closed position and an open position. A fluid flow path can be provided when the valve is in the open position, the fluid flow path extending from an interior of the inflatable structure through the inflation lumen and through the valve. The valve can block the fluid flow path when the valve is in the closed position. The valve can include a temperature sensitive element. The temperature sensitive element can force the valve into the open position when a temperature exceeds a first value. The temperature sensitive element can allow the valve to return to the closed position when the temperature falls below a second value.
In this aspect, the valve can include a movable member and a body, a first surface of the movable member contacting a second surface of the body when the valve is in the closed position, the first surface of the movable member being spaced apart from the second surface of the body when the valve is in the open position. Also, the valve can include a spring, the spring biasing the first surface of the movable member towards the second surface of the body.
In another aspect, the invention provides a method of automatically protecting an inflatable device during sterilization. The method can include a step of providing the device with a temperature sensitive valve that automatically opens when a temperature exceeds a first value. The method can further include a step of exposing the device to an environment that will sterilize the device, the environment being characterized by a temperature above the first value. When the temperature exceeds the first value, the valve can automatically open and permit fluid in the inflatable device to escape into the environment.
In another aspect, the invention provides a medical device including an inflatable structure and a valve. The inflatable structure can be configured for positioning in a human patient. The valve can be in fluid communication with the inflatable structure. The valve can include a member that is movable between an open position and a closed position. The valve can prevent fluid from escaping the inflatable structure when the member is in the closed position. The valve can permit fluid to escape the inflatable structure when the member is in the open position. The valve can include a resilient element. The resilient element can provide a first force that biases the member towards the closed position. The valve can include a temperature sensitive element. The temperature sensitive element can generate a second force that biases the member towards the open position. The first force can be greater than the second force when the ambient temperature is below a first value. The first force can be smaller than the second force when the ambient temperature is above a second value. An end portion of the member can be accessible to an environment external to the valve. The member can be movable to the open position by applying pressure to the end portion of the member.
In this aspect, the second force can be substantially equal to zero when the ambient temperature is below the first value.
Also in this aspect, the temperature sensitive element can comprise a nickel titanium alloy.
Also in this aspect, the temperature sensitive element can be characterized by a first length when the ambient temperature is below the first value, and the temperature sensitive element can be characterized by a second length when the ambient temperature is above the second value. The first length can be longer than the second length.
Also in this aspect, the valve can include a body. The body can define an internal passage that extends through the body. Also, the body can define a first shoulder. Also, the member can define a second shoulder. The first and second shoulders can be in contact when the member is in the closed position. The first and second shoulders can be spaced apart when the member is in the open position. Also, the device can include a cap fixed to one end of the body. Also, the device can include a post fixed to one end of the member. Also, the temperature sensitive element can have a first end, a second end, and a central portion. The first and second ends of the temperature sensitive element can be fixed to the cap. The central portion of the temperature sensitive element can contact the post. Also, the post can define a slot. The central portion of the temperature sensitive element can extend through the slot. Also, the cap can include a base, a body, and at least one clamp. Also, the clamp can be disposed between a portion of the base and a portion of the body. Also, the end of the temperature sensitive element can be fixed to the clamp. Also, the second value can be greater than or equal to seventy degrees Celsius.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description wherein several embodiments are shown and described, simply by way of illustration of the best mode of the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not in a restrictive or limiting sense, with the scope of the application being indicated in the claims.